The present invention relates to drying of biological specimens and refers more particularly to improved method and apparatus by which such drying can be carried out.
In certain laboratory procedures, it is required to separate and concentrate biological material from a solvent-containing specimen, i.e., dry the specimen in preparation for study of the dried specimen material by amino acid analysis, gas chromatography, mass spectroscopy and like. This can be done, e.g., with the Savant Instruments, Inc. Automated SPEEDVAC Systems A160 or A290, which apparatus includes a vacuum centrifuge of the type disclosed in commonly owned U.S. Pat. No. 4,226,669, a vacuum pump for imposing a vacuum on the interior of a drying chamber, i.e., the centrifuge, a refrigerated trap to which solvent vapors evolving in the drying cycle pass for condensing of the same, a microprocessor for controlling the drying apparatus, and conduit tubing as well as a pair of control valves for establishing of blocking communication or conduit flow courses in the systems for various reasons attending the drying operation and cycle.
Both these systems use a three-way drying chamber vacuum control valve disposed in the conduit connecting the drying chamber with the pump and located proximal or adjacent the drying chamber. This three-way valve is a normally open type which when open connects the chamber with ambient atmosphere or an inert gas source. When closed, the valve connects the chamber with the condensate trap located downstream a distance of the chamber. These systems also use a two-way pump bleeder valve adjacent the vacuum pump and on the upstream side of the pump which valve also is a normally open type connected to the conduit leg leading to the pump and cold trap, and when closed, disconnecting the pump and condensation trap from the atmosphere.
With these systems, the vacuum pump during drying cycle is always connected to the drying chamber so that any solvent vapor escaping condensation in the trap can pass therefrom and eventually into the vacuum pump. The solvent contaminates the oil in the pump which necessitates frequent oil change and it also can cause corrosion of pump internal structure. Further, the vacuum pumps in these systems generally will operate at a given constant vacuum level which can be one below that at which certain highly volatile solvents can "bump" from the specimen and carry biological material away from the specimen--a result to be avoided since valuable specimen material constituents can be lost to the detriment of the eventual analysis to which the dried specimen is to be subjected.